Planetary Hour Calculator

The Chaldean Order — A 2,500-Year-Old Tradition

The planetary hour system traces back to the Chaldean astronomers of ancient Mesopotamia around 500 BCE. They observed that the seven visible celestial bodies — Saturn, Jupiter, Mars, the Sun, Venus, Mercury, and the Moon — moved at different speeds across the sky, and they arranged them in order from slowest (Saturn, farthest) to fastest (Moon, closest). This sequence, known as the Chaldean order, became the backbone of classical astrology and the seven-day week. Each hour of the day is assigned to one of these planets in a repeating cycle, and the planet ruling the first hour of daylight gives the day its name: the Sun rules Sunday, the Moon rules Monday, Mars rules Tuesday (mardi in French, martes in Spanish), Mercury rules Wednesday (mercredi), Jupiter rules Thursday (jeudi), Venus rules Friday (vendredi), and Saturn rules Saturday. This naming convention survives across Indo-European and Semitic languages and calendars worldwide.

How to Read Your Planetary Hours Schedule

When you enter your date and location into the Planetary Hours Calculator, it computes the exact time of your local sunrise and sunset using the Jean Meeus Chapter 25 solar algorithm — the same standard formula used in professional astronomical ephemerides. It then splits the daylight period (sunrise to sunset) into 12 equal planetary hours and the nighttime period (sunset to next sunrise) into 12 more. The result panel shows you three key pieces of information: (1) the current planetary hour and when it ends, so you know what influence is active right now; (2) today's day ruler, which is the planet governing the first hour after sunrise; and (3) a full 24-hour schedule browsable by Day or Night tab, with each hour's start time, end time, and ruling planet clearly listed. Planetary hours are location-specific, so the same date yields completely different schedules in New York compared to Tokyo or London.

Practical Uses for Planetary Hours

While planetary hours trace their roots to classical astrology and Hermetic tradition, many people use them as a practical decision-making framework for daily life. During a Mercury hour — ideal for analytical work, writing, studying, or making important phone calls. A Venus hour favours creative projects, social gatherings, or anything involving beauty and harmony. Jupiter hours are associated with expansion and opportunity — consider scheduling a business pitch, a job interview, or a financial decision. Mars hours carry an active, energetic quality suited to physical exercise, tackling difficult tasks, or starting a new project. Saturn hours lean toward discipline and structure — ideal for planning, organizing, or long-term thinking. The Moon hour governs emotions and domestic matters, while the Sun hour supports visibility, leadership, and self-expression. Even if you approach it skeptically, the planetary hour rhythm can serve as a simple mindfulness prompt — a reminder to align your task with the energy you want to bring to it.

Track lunar phases to complement your planetary hour timing → MoonSync Lunar Calendar

How This Calculator Works — and Why It's Private

The Planetary Hours Calculator runs entirely in your browser. Your location coordinates are never sent to any server — they stay on your device and are used only to compute local sunrise and sunset times. The core algorithm is Jean Meeus's Chapter 25 simplified solar position formula, which provides ±1 minute accuracy for dates between 1900 and 2100 CE. Once sunrise and sunset are determined, the daylight period is divided into 12 equal segments and the nighttime into 12, with planets assigned in Chaldean order starting from the day ruler. The calculator handles edge cases gracefully: if you are above approximately 66.5° latitude during polar day or polar night seasons when the sun never rises or sets, it will show a POLAR_REGION notification and suggest you try a nearby latitude or a different date. All computation is deterministic and repeatable — the same inputs always produce the same result.

The sunrise and sunset times used here come from our Solar Calculator — see golden hour and twilight data → Solar Calculator